Degradable particulates as friction reducers for the flow of solid particulates and associated methods of use

ABSTRACT

Particulate compositions that comprise macro-particulates, and degradable particulates in an amount sufficient to reduce friction between the macro-particulates, the degradable particulates having a mean particle diameter of at least about 20 times smaller than the mean particle diameter of the macro-particulates are disclosed herein. Also disclosed are fluids that comprise a liquid component, and a particulate composition, the particulate composition comprising macro-particulates and degradable particulates having a mean particle diameter of at least about 20 times smaller than the mean particle diameter of the macro-particulates, wherein the degradable particulates are present in the particulate composition in an amount sufficient to reduce friction between the macro-particulates. Methods of using the particulate compositions and fluids are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention is related to U.S. patent application Ser. No.11/393,607, entitled “Degradable Particulates as Friction Reducers forthe Flow of Solid Particulates and Associated Methods,” filed on evendate herewith, the entire disclosure of which is incorporated herein byreference.

BACKGROUND

The present invention relates to methods and compositions for improvingparticulate flow. More particularly, the present invention relates tothe use of degradable particulates as friction reducers that may reducethe potential stresses caused by increased particulate loading influids.

Fluids comprising solid particulates often are used in a variety ofapplications performed in subterranean formations. Such applicationsinclude, but are not limited to, drilling operations, productionstimulation operations (e.g., hydraulic fracturing) and well completionoperations (e.g., gravel packing). Fluids containing solid particulatesare also used in a variety of surface applications as well.

The term “particulate(s),” as used herein, refers to particles having adefined physical shape as well as those with irregular geometries,including any particles having the physical shape of platelets,shavings, fibers, flakes, ribbons, rods, strips, spheres, spheroids,toroids, pellets, tablets, or any other physical shape.

In a hydraulic-fracturing operation, a type of fluid, commonly referredto as a “fracturing fluid”, may be placed in a subterranean formation ator above a pressure sufficient to create or enhance at least onefracture in the formation. Enhancing a fracture includes enlarging apre-existing fracture in the formation. In some instances, ahydraulic-fracturing operation may involve pumping a proppant-free,viscous fluid (commonly referred to as a “pad fluid”) into asubterranean formation faster than the fluid can escape into theformation so that the pressure in the formation rises and the formationbreaks, creating or enhancing one fractures in the subterraneanformation. At a desired time, for example, once the fracture is formedor enlarged, particulates (commonly referred to as “proppant”) aregenerally placed into the fracture to form a proppant pack that mayprevent the fracture from closing when the hydraulic pressure isreleased and thereby potentially enhance the conductivity of theformation.

In a gravel-packing operation, particulates (commonly referred to as“gravel”) may be carried to a portion of a well bore penetrating asubterranean formation by a carrier fluid, inter alia, to reduce themigration of unconsolidated formation particulates (e.g. formation sand)into the well bore. The carrier fluid may be viscosified, inter alia, toenhance certain properties (e.g., particulate suspension). Once thegravel has been placed into a gravel pack in the well bore or in aportion of the subterranean formation, the viscosity of the carrierfluid may be reduced, whereupon it may be returned to the surface andrecovered. As used herein, the term “gravel pack” refers to theplacement of particulates in and/or neighboring a portion of asubterranean formation so as to provide at least some degree of sandcontrol, such as by packing the annulus between the subterraneanformation and a screen disposed in the subterranean formation withparticulates of a specific size designed to prevent the passage offormation sand. Gravel packs often are used to stabilize the formationwhile causing minimal impairment to well productivity. While screenlessgravel-packing operations are becoming increasingly common, traditionalgravel-packing operations commonly involve placing a gravel-pack screenin the well bore neighboring a desired portion of the subterraneanformation, and packing the surrounding annulus between the screen andthe well bore with gravel particulates that are sized to prevent andinhibit the passage of formation solids through the gravel pack withproduced fluids. The gravel-pack screen is generally a filter assemblyused to support and retain the gravel particulates placed during thegravel-packing operation. A wide range of sizes and screenconfigurations are available to suit the characteristics of the wellbore, the production fluid, and the portion of the subterraneanformation.

In some situations, hydraulic-fracturing operations and gravel-packingoperations may be combined into a single operation to stimulateproduction and to reduce the production of unconsolidated formationparticulates. Such treatments are often referred to as “frac-pack”operations. In some cases, these treatments are completed with agravel-pack screen assembly in place with the fracturing fluid beingpumped through the annular space between the casing and screen. In sucha situation, the fracturing operation may end in a screen-out conditioncreating an annular gravel pack between the screen and casing.

In these and other operations involving a particulate-laden fluid, anupper limit may exist as to the optimum amount of particulates that canbe suspended and successfully carried in the fluid. The flow ofdispersions of particulates in a liquid may become increasinglydifficult as the volume fraction of particulates increases, e.g., boththe steady shear viscosity and the residual stress within the dispersionmay increase as the volume fraction of particles increases. The increasein steady shear viscosity and/or residual stress generally is notlinear; rather, it generally increases as the solids content approachesmaximum packing (for fluids having a particle size distribution that ismonodisperse, maximum packing of solids is known to be about 66% byvolume of the dispersion). During the flow of concentrated dispersionsof solids through a container or channel (e.g., a laboratory test tubeor a subterranean fracture), the solid particles may form bridges acrossthe inner diameter of the container or channel, thereby blocking orimpairing the flow. This tendency to form bridges may increase asresidual stress within the dispersion increases.

When this phenomenon occurs during a conventional subterraneanapplication, e.g., a fracturing operation, this undesirable bridging ofproppant particulates across the width of a fracture in a formation maytend to prematurely halt the deposit of the proppant particulates withinthe fracture. This bridging may block further flow of fracturing fluidinto the fracture (thereby preventing continued propagation of thefracture). In other cases, the fracturing fluid may succeed in flowingaround the blockage, and may continue (without the proppantparticulates) to penetrate into the formation, thereby continuing topropagate the fracture for a time. In this latter case, however, theportion of the fracture that extends beyond the bridged proppantparticulates generally will lack proppant particulates, and likely willundesirably re-close shortly after the termination of the fracturingoperation, because it may lack the support necessary to maintain itsintegrity.

The addition of small silica particles (e.g., from nanometer to micronsize) to particulate-laden fluids has been used to help alleviatestresses caused by increased particulate loading. For instance, theaddition of small silica particles may allow increased particulateloading in a fluid, for example, up to or greater than about 55% solidsby volume. While these small silica particles generally allow increasedparticulate loading, their use may have some drawbacks. For instance,after introduction into a well bore, these small silica particles maylodge themselves in formation pores, preslotted liners, screens,proppant packs, and/or gravel packs, preventing or reducing fluid flowthere through. This may result in an undesirable reduction in wellproductivity, particularly in low permeability formations.

SUMMARY

The present invention relates to methods and compositions for improvingparticulate flow. More particularly, the present invention relates tothe use of degradable particulates as friction reducers that may reducethe potential stresses caused by increased particulate loading influids.

In one embodiment, the present invention provides a fluid that comprisesa liquid component, and a particulate composition, the particulatecomposition comprising macro-particulates and degradable particulateshaving a mean particle diameter of at least about 20 times smaller thanthe mean particle diameter of the macro-particulates, wherein thedegradable particulates are present in the particulate composition in anamount sufficient to reduce friction between the macro-particulates.

Another embodiment of the present invention provides a particulatecomposition comprising macro-particulates, and degradable particulatesin an amount sufficient to reduce friction between themacro-particulates, the degradable particulates having a mean particlediameter of at least about 20 times smaller than the mean particlediameter of the macro-particulates.

The features and advantages of the present invention will be apparent tothose skilled in the art. While numerous changes may be made by thoseskilled in the art, such changes are within the spirit of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates to methods and compositions for improvingparticulate flow. More particularly, the present invention relates tothe use of degradable particulates as friction reducers that may reducethe potential stresses caused by increased particulate loading influids. While the compositions and methods of the present invention areuseful in a variety of subterranean applications, they may beparticularly useful in subterranean treatment operations (includinggravel packing, fracturing, and frac-packing operations) that utilizefluids containing particulates (e.g., proppant, gravel, etc.).

The fluids of the present invention generally comprise a liquidcomponent and a particulate composition, wherein the particulatecomposition comprises macro-particulates and degradable particulateshaving a mean particle diameter of at least about 20 times smaller thanthe mean particle diameter of the macro-particulates. The degradableparticulates should be present in the particulate composition an amountsufficient to reduce friction between the macro-particulates. Forexample, the degradable particulates may enhance the flow of the fluiddue to this reduction in friction the macro-particulate and a resultantreduction in viscosity and residual stress of this particulate-ladenfluid. In some embodiments, the degradable particulates may have a meanparticle diameter in the range of from about 10 nanometers to about 30microns.

Where the methods and compositions of the present invention are used insubterranean applications, the liquid component may be any liquidcomponent suitable for transporting solids that is commonly included insubterranean applications, including, but not limited to, water, brines,viscosified fluids, foams, aqueous gels, viscoelastic surfactant gels,emulsions, combinations thereof, and other fluids suitable fortransporting solids. Where the liquid component comprises an aqueousgel, the aqueous gel generally comprises water and a gelling agent. Inone embodiment, the aqueous gel further may comprise water, a gellingagent, and, optionally, a crosslinking agent that crosslinks at least aportion of the molecules of the gelling agent further increasing theviscosity of the fluid, which further may affect the fluid's ability tosuspend solids. Where the liquid component comprises an emulsion, theemulsion may comprise two or more immiscible liquids; for example, theemulsion may comprise an aqueous gel and a liquefied, normally gaseousfluid (e.g., carbon dioxide). In certain embodiments, it may bedesirable to increase the viscosity of a fluid so as, inter alia, toreduce fluid loss into the subterranean formation and reduce thesedimentation of suspended particles. Generally, the liquid componentmay be present in the fluids of the present invention in an amount inthe range of from about 32% to about 99% by volume of the fluid, whenmeasured at the surface, prior to placement of the fluid in asubterranean formation. In some embodiments, the liquid component may bepresent in an amount in the range of from about 45% to about 97% volumeof the fluid.

The particulate composition present in the fluids of the presentinvention generally comprises macro-particulates and degradableparticulates, wherein the degradable particulates have a mean particlediameter of at least about 20 times smaller than the mean particlediameter of the macro-particulates. In some embodiments, the degradableparticulates may have a mean particle diameter in the range of fromabout 10 nanometers to about 30 microns. Generally, the particulatecomposition may be present in the fluids of the present invention in anamount in the range of from about 1% to about 68% by volume of thefluid, when measured at the surface, prior to placement of the fluid ina subterranean formation. In some embodiments, the particulatecomposition may be present in an amount in the range of from about 3% toabout 55% by volume of the fluid. In some embodiments, the particulatecomposition may be preset in an amount in the range of from about 50% toabout 68% by volume of the fluid. The amount of the particulatecomposition to include in the fluids of the present invention varydependent on a variety of factors, including the particular application,such as moving solid particulate slurries in surface applications or ina fluid for use downhole.

Any particulate material suitable for use in subterranean applications(for example, as proppant particulates, gravel particulates, etc.) maybe suitable for use as the macro-particulates. Suitable particulatematerials include, but are not limited to, sand; bauxite; ceramicmaterials; glass materials; polymer materials; thermoplasticfluoropolymers (e.g., Teflon® (tetrafluoroethylene) materials); nutshell pieces; seed shell pieces; fruit pit pieces; wood; compositeparticulates; cured resinous particulates comprising nut shell pieces,seed shell pieces, inorganic fillers, and/or fruit pit pieces; andcombinations thereof.

Though a “mean particle diameter” may be determined for the particulatesof any bulk solid, the individual particulates of the bulk solidgenerally exist in a range of sizes, including a portion of “fines” thatmay have a diameter about 20 times smaller than the “mean particlediameter” of the bulk solid. Though such fines of the macro-particulatesmay be present in the particulate composition of the fluids of thepresent invention, the concentration of fines having the desired size(e.g., at least about 20 times smaller than the average diameter)generally will be sufficiently small that the fines will not impact thephysical properties of the fluids of the present invention. Generally,the macro-particulates may have a mean particular diameter suitable fora particular application. In some embodiments, the macro-particulatesmay have mean particle diameter in the range of from about 6 mesh toabout 400 mesh, U.S. Sieve Series. In particular embodiments, suitablemacro-particulates may have mean particle diameters of 6/12 mesh, 8/16,12/20, 16/30, 20/40, 30/50, 40/60, 40/70, or 50/70 mesh. Generally, themacro-particulate should have a mean particle diameter at least about 20times as large as that of the degradable particulates. Those of ordinaryskill in the art will appreciate that the macro-particulates may bemonodisperse or polydisperse.

The macro-particulates may be present in the particulate composition inan amount desired for a particular application. In some embodiments, themacro-particulates may be present in the particulate composition in anamount in the range of from about 80% to about 99.75% by volume of theparticulate composition. In some embodiments, the macro-particulates maybe present in the particulate composition in an amount in the range offrom about 90% to about 98% by volume of the particulate composition. Insome embodiments, the macro-particulates may be present in theparticulate composition in an amount in the range of from about 95% toabout 97% by volume of the particulate composition.

The degradable particulates included in the particulate composition ofthe fluids of the present invention should be capable of undergoing anirreversible degradation downhole. Because these degradable particulatesshould undergo an irreversible degradation downhole, they generallyshould not undesirably plug fluid flow pathways in the formation.

As used in this disclosure, the term “irreversible” means that thedegradable particulates once degraded should not recrystallize orreconsolidate downhole. As used herein, the term “degradation,” or“degradable,” refers to the conversion of materials into smallercomponents, intermediates, or end products by the result ofsolubilization, hydrolytic degradation, biologically formed entities(e.g., bacteria or enzymes), chemical reactions, thermal reactions,reactions induced by radiation, or any other suitable mechanism. As usedherein, “hydrolytic degradation” refers to both heterogeneous (or bulkerosion) and homogenous (or surface erosion), and any stage ofdegradation between these two by the action of water on the particulate.

The degradable particulates included in the particulate composition ofthe fluids of the present invention may comprise any degradablematerials suitable for use in the desired application. Degradablematerials that may be used in conjunction with the present inventioninclude, but are not limited to, degradable polymers, dehydratedcompounds, oil-soluble materials, water-soluble compounds, and mixturesthereof. The term “polymer(s)”, as used herein, does not imply anyparticular degree of polymerization; for instance, oligomers areencompassed within this definition. In some instances, the degradablematerial may be capable of releasing a desirable degradation product,e.g., an acid or a base, during its degradation. Among other things, thedegradable materials capable of releasing an acid should degrade after adesired time to release an acid, for example, to degrade a filter cakeor to reduce the viscosity of a fluid.

In certain embodiments, the degradable materials may comprise degradablepolymers. The degradability of a polymer depends at least in part on itsbackbone structure. For instance, the presence of hydrolyzable and/oroxidizable linkages in the backbone often yields a material that willdegrade as described herein. The rates at which such polymers degradeare dependent on the type of repetitive unit, composition, sequence,length, molecular geometry, molecular weight, morphology (e.g.,crystallinity, size of spherulites, and orientation), hydrophilicity,hydrophobicity, surface area, and additives. Also, the environment towhich the polymer is subjected may affect how it degrades, e.g.,temperature, presence of moisture, oxygen, microorganisms, enzymes, pH,and the like. Generally, the degradable polymers used in the presentinvention should be formulated and have a molecular weight such thatthey are solid at room temperature and do not generally plasticize atroom temperature by the addition of oil or an aqueous phase.

Suitable examples of degradable polymers that may be used in accordancewith the present invention include, but are not limited to,homopolymers, random, block, graft, and star- and hyper-branchedpolymers. Examples of suitable degradable polymers that may be used inconjunction with the methods of this invention include, but are notlimited to, polysaccharides (such as dextran or cellulose); chitin;chitosan; proteins; aliphatic polyesters; polylactic acids;poly(glycolides); poly(ε-caprolactones); poly(hydroxy ester ethers);poly(hydroxybutyrates); poly(anhydrides); polycarbonates;poly(orthoesters); poly(amino acids); poly(ethylene oxides);poly(phosphazenes); poly etheresters, polyester amides, polyamides, andcopolymers or blends of any of these degradable materials. The term“copolymer,” as used herein, is not limited to the combination of twopolymers, but includes any combination of polymers, e.g., terpolymers,block copolymers, graft copolymers, star block copolymers, and the like.Of these suitable polymers, polylactic acids, andpoly(lactide)-co-poly(glycolide) copolymers may be used, in someembodiments. As used herein, “poly(lactic acid)” refers to a polymerthat may be synthesized from lactic acid, for example, by a condensationreaction or by the ring-opening polymerization of a cyclic lactidemonomer, and is sometimes referred to as “PLA,” “polylactate,” or“polylactide.”

Other degradable polymers that are subject to degradation also may besuitable. One's choice may depend on the particular application and theconditions involved. Other guidelines to consider include thedegradation products that result, the time required for the requisitedegree of degradation, the desired result of the degradation (e.g.,voids), temperature, time, and additives that may be used.

Where degradable polymers are included in the degradable material, thedegradable polymers may at least partially prevent flow back of themacro-particulates after introduction of the particulate compositioninto the subterranean formation. At temperatures above the glasstransition temperature (“T_(g)”), the degradable polymers may haveproperties (e.g., tackiness) that may act to at least partially preventthe flow back. The degradable polymers may at least partially preventflow back for a certain period of time, for example, until thedegradable polymer is fully degraded. Poly(lactic acid), an example of aparticular degradable polymer, generally has a T_(g) in the range offrom about 30° C. to about 60° C. The temperature may be reached by theheating of the degradable material to the bottom hole statictemperature, for example, after introduction into the subterraneanformation.

In certain embodiments, plasticizers may be included in the degradablematerial used in the methods of the present invention. Among otherthings, the incorporation of plasticizers into the degradable materialshould decrease the T_(g) of the degradable material. The plasticizersmay be present in an amount sufficient to provide the desiredcharacteristics, for example, a desired tackiness to the generateddegradable materials. Tackiness may be desirable, for example, to atleast partially prevent flow back of the macro-particulates. Generally,the plasticizer, in some embodiments, should not plasticize the polymerat surface temperature before pumping of the particulate-laden fluidsinto a well bore, but should plasticize the polymer after theparticulate composition has been placed into a subterranean formationand/or packed into a fracture. If premature plasticization occurs, thestress-reducing effect of the degradable particulates may be reduced. Inaddition to the other qualities above, the plasticizers may enhance thedegradation rate of the degradable materials. The plasticizers, if used,are preferably at least intimately incorporated within the degradablematerials. An example of a suitable plasticizer for polylactic acidwould include oligomeric lactic acid. Examples of plasticizers usefulfor this invention include, but are not limited to, polyethylene glycol;polyethylene oxide; oligomeric lactic acid; citrate esters (such astributyl citrate oligomers, triethyl citrate, acetyltributyl citrate,and acetyltriethyl citrate); glucose monoesters; partially fatty acidesters; PEG monolaurate; triacetin; poly(e-caprolactone);poly(hydroxybutyrate); glycerin-1-benzoate-2,3-dilaurate;glycerin-2-benzoate-1,3-dilaurate; bis(butyl diethylene glycol)adipate;ethylphthalylethyl glycolate; glycerin diacetate monocaprylate; diacetylmonoacyl glycerol; polypropylene glycol (and epoxy derivatives thereof);poly(propylene glycol)dibenzoate, dipropylene glycol dibenzoate;glycerol; ethyl phthalyl ethyl glycolate; poly(ethyleneadipate)distearate; di-iso-butyl adipate; and combinations thereof. Thechoice of an appropriate plasticizer will depend on the particulardegradable material utilized. It should be noted that, in certainembodiments, when initially formed, the degradable material may besomewhat pliable. But once substantially all of the solvent has beenremoved, the particulates should harden. More pliable degradablematerials may be beneficial in certain chosen applications. The additionof presence of a plasticizer can affect the relative degree ofpliability. Also, the relative degree of crystallinity and amorphousnessof the degradable material can affect the relative hardness of thedegradable materials.

Dehydrated compounds also may be suitable degradable materials that maybe included in the degradable particulates included in the particulatecomposition of the fluids of the present invention. Suitable dehydratedcompounds include those materials that will degrade over time whenrehydrated. For example, a particulate solid dehydrated salt or aparticulate solid anhydrous borate material that degrades over time maybe suitable. Specific examples of particulate solid anhydrous boratematerials that may be used include but are not limited to anhydroussodium tetraborate (also known as anhydrous borax), and anhydrous boricacid. These anhydrous borate materials are only slightly soluble inwater. However, with time and heat in a subterranean environment, theanhydrous borate materials react with the surrounding aqueous fluid andare hydrated. The resulting hydrated borate materials are substantiallysoluble in water as compared to anhydrous borate materials and as aresult degrade in the aqueous fluid.

Oil-soluble materials also may be a suitable degradable material.Suitable oil-soluble materials include natural or synthetic polymers,such as, for example, poly(butadiene), polyisoprene, polyether urethane,polyester urethane, and polyolefins (such as polyethylene,polypropylene, polyisobutylene, and polystyrene), and copolymers andblends thereof. Where oil-soluble materials are used, the particularoil-soluble material and liquid component should be selected so that thewater-soluble material does not undesirable degrade prior to providingthe desired friction reduction. For example, oil-soluble materials maybe suitable for use in an aqueous carrier fluids and/or water-baseddrilling or drill-in fluids. Where oil-soluble materials are used, insome embodiments, the oil-soluble materials may be degraded, forexample, by the fluids (e.g., oil) subsequently produced from theformation. If used in a drilling fluid, the oil-soluble materialspresent in the filtercake formed with the drilling fluid also may bedissolved by the subsequent production of oil.

Water-soluble materials also may be a suitable degradable material.Suitable water-soluble materials include, but are not limited to,calcium carbonate, fused magnesium oxide, calcium oxide. Wherewater-soluble materials are used, the particular water-soluble materialand liquid component should be selected so that the water-solublematerial does not undesirably degrade prior to providing the desiredfriction reduction. For example, water-soluble materials may be used inoil-based drilling fluids, oil-based fracturing, fluids, and oil-basedgravel packing fluids. The water-soluble materials should then dissolvefrom contact with water present in the subterranean formation.Additionally, water-soluble materials also may be used in aqueousfluids, if a desirable level of friction reduction may occur prior tosolubilization of the water-soluble material in the aqueous fluid.

Blends of certain degradable materials and other compounds may also besuitable. One example of a suitable blend of materials is a mixture ofpolylactic acid and sodium borate where the mixing of an acid and basecould result in a neutral solution where this is desirable. Anotherexample would include a blend of polylactic acid and boric oxide. Inchoosing the appropriate degradable material or materials, one shouldconsider the degradation products that will result. The degradationproducts should not adversely affect subterranean operations orcomponents.

The choice of degradable material to include in the degradableparticulates also can depend, at least in part, on the conditions of thewell, e.g., well bore temperature. For instance, lactides have beenfound, in certain embodiments, to be suitable for lower temperaturewells, including those within the range of 60° F. to 150° F. Polylacticacid and dehydrated compounds may be suitable for higher temperaturewells, for example those within the range of from 180° F. to 250° F. oreven higher. Those of ordinary skill in the art will recognize, that thedegradation rate of the degradable materials is generally related totemperature so that higher temperature wells generally should result inless residence time of the degradable material downhole. Also, in someembodiments, a preferable result is achieved if the degradableparticulate degrades slowly over time as opposed to instantaneously. Insome embodiments, it may be desirable when the degradable particulatedoes not substantially degrade until after the degradable particulatehas been substantially placed in a desired location within asubterranean formation.

The degradable particulates have a mean particle diameter of at leastabout 20 times smaller than the mean particle diameter of themacro-particulates. In some embodiments, the degradable particulateshave a mean particle diameter of at least about 50 times smaller thanthe mean particle diameter of the macro-particulates. In someembodiments, the degradable particulates have a mean particle diameterof at least about 100 times smaller than the mean particle diameter ofthe macro-particulates. In some embodiments, the degradable particulateshave a mean particle diameter of at least about 1,000 times smaller thanthe mean particle diameter of the macro-particulates. In someembodiments, the degradable particulates have a mean particle diameterof at least about 3,000 times smaller than the mean particle diameter ofthe macro-particulates. In some embodiments, the degradable particulatesmay have a mean particle diameter in the range of from about 10nanometers to about 30 microns. The exact size of the degradableparticulates used depends on the degradable particulate chosen, thedensity of the different particulate compositions, the size of themacro-particulates, and a number of other factors.

The degradable particulates should be present in the particulatecomposition in an amount sufficient to provide reduce friction betweenthe macro-particulates. In some embodiments, the degradable particulatesare present in the particulate composition in an amount in the range offrom about 0.25% to about 20% by volume of the particulate composition.In some embodiments, the degradable particulates are present in theparticulate composition in an amount in the range of from about 2% toabout 10% by volume of the particulate composition. In some embodiments,the degradable particulates are present in the particulate compositionin an amount in the range of from about 3% to about 5% by volume of theparticulate composition. The amount the degradable particulates to useis based on a number of factors including, particle size and density ofthe different particulate compositions.

Optionally, the fluids of the present invention also may include one ormore of a variety of additional additives such as breakers, stabilizers,fluid loss control additives, clay stabilizers, bactericides, corrosioninhibitors, surfactants, oxidizers, combinations thereof, and the like.For example, certain surfactants (e.g., sodium n-dodecyl sulfate,cetyltrimethylammonium bromide, betaines, etc.) may be used as frictionreducers in combination with the degradable particulates. Those ofordinary skill in the art, with the benefit of this disclosure, will beable to select the appropriate additional additives to include in thefluids for a particular application.

The fluids of the present invention may be used in surface andsubterranean applications where reduction in friction caused byparticulate loading is desired. For example, the methods andcompositions of the present invention may be particularly suitable foruse in fracturing and/or gravel packing operations. An example of amethod of the present invention comprises: providing a fluid comprisinga liquid component and a particulate composition, wherein theparticulate composition comprises macro-particulates and degradableparticulates having a mean particle diameter of at least about 20 timessmaller than the mean particle diameter of the macro-particulates; andintroducing the fluid into a subterranean formation. The degradableparticulates are generally present in the particulate composition in anamount sufficient to reduce friction between the macro-particulates. Incertain embodiments, the liquid component may further comprise aviscosifying agent (e.g., xanthan, guar or guar derivatives, cellulosederivatives, a viscoelastic surfactant, etc.) that may aid in suspendingthe particulate composition in the fluid, thereby enhancing theuniformity of the suspension.

As discussed previously, the methods of the present invention may beparticularly suitable for use in fracturing and/or gravel packingoperations. In the fracturing embodiments, the method further comprisesintroducing the fluid into the subterranean formation at or above apressure sufficient to create or enhance one or more fractures in thesubterranean formation. In such fracturing and gravel packingoperations, at least a portion of the particulate composition of thefluids of the present invention may be deposited within and/orneighboring the subterranean formation, e.g., a proppant pack or agravel pack. For example, in the fracturing embodiments, the fluid maybe introduced into the subterranean formation so that at least a portionof the particulate composition may form a proppant pack in the one ormore factures. In the gravel packing embodiments, the fluid may beintroduced in the subterranean formation so that at least a portion ofthe particulate composition may form a gravel pack in and/or neighboringthe portion of the subterranean formation.

When used in such subterranean applications, the presence of thedegradable particulates in the particulate composition of the fluids ofthe present invention may impart a lubricating effect upon themacro-particulates as the fluids of the present invention flow withinthe subterranean formation. This lubricating effect may reduce theviscosity and/or yield point of a proppant pack or gravel pack during,or after its placement in the formation by the fluids of the presentinvention. Further, this lubricating effect may permit a fluid of thepresent invention comprising a dispersion of degradable andmacro-particulates to penetrate further into a subterranean formationduring a treatment operation, thereby increasing the amount of solidsthat a fluid of the present invention successfully may deposit withinthe formation. As discussed above, certain degradable particulates(e.g., those comprising degradable polymers) may at least partiallyprevent flow back of the macro-particulates after introduction of theparticulate composition into the subterranean formation. For example, attemperatures above T_(g), the degradable polymers may have properties(e.g., tackiness) that may act to at least partially prevent the flowback.

Another example of a method of the present invention is a method ofenhancing the flow of drill cuttings comprising: providing a drillingfluid; drilling at least a portion of a well bore using at least thedrilling fluid, wherein the drilling produces drill cuttings in thedrilling fluid; and adding degradable particulates to the drilling fluidin an amount sufficient to reduce friction between the drilling cutting,wherein the degradable particulates have a mean particle diameter of atleast about 20 times smaller than the mean particle diameter of themacro-particulates. Among other things, the degradable particulates mayfacilitate the flow back of the drill cutting and also prevent or reduceproblems encountered during drilling operations (e.g., stuck pipe).

To facilitate a better understanding of the present invention, thefollowing example(s) of certain aspects of some embodiments are given.In no way should the following example(s) be read to limit, or define,the scope of the invention.

EXAMPLE 1

A sample composition was prepared by dispersing 20/40 Brady sand(density=2.65 g/cc) by hand, using a spatula, into a 1% solution ofcarboxymethyl hydroxylpropylguar until the dispersion was visiblyuniform. To this sample composition, degradable polylactic acidparticulates having a mean particle diameter of 3 microns were dispersedby hand, using a spatula. Accordingly, the sample composition comprised55% total solids volume that comprised 5% by volume of 3 microndegradable polylactic acid particulates, and 95% by volume ofmacro-particulates of Brady sand.

The sample composition was then observed. The apparent viscosity of thesample composition was observed to have substantially reduced withaddition of the degradable particulates. A reduction in friction betweenthe particulates of Brady sand was also observed, due to the improvedflowability and pourability of the sample composition after the additionof the degradable particulates.

EXAMPLE 2

20/40 Brady sand (density=2.65 g/cc) having a mean particle diameter of490 microns, and found to have no detectable fines having particlediameters below 130 microns, was mixed with varying proportions ofpolylactic acid micro-particulates (density=1.25 g/cc) having averageparticle diameter of 14 microns. The sand particles and polylactic acidmicro particles were dispersed by hand, using a spatula, into a 0.5%solution in water of carboxymethyl hydroxypropylguar until thedispersion was visibly uniform. These sample compositions were thentested with a Fann Yield Stress Adapter, described in U.S. Pat. No.6,874,353, to determine their residual stress and viscosity in a fluidat different solid loadings. The testing was done as described in U.S.Pat. No. 6,874,353.

Sample Composition Nos. 1 to 3 comprised aqueous dispersions of 45%,52.5% and 57% total solids volume, respectively in a 0.5% carboxymethylhydroxypropylguar solution in water. The total solid volume entirelycomprised 20/40 Brady sand. The apparent viscosities of SampleCompositions 1 through 3 were measured to be 13.9, 33.8 and 58.1Pa-second, respectively. The residual stress of Sample Compositions 1through 3 was measured to be 0, 9 and 27 Pa, respectively.

Sample Composition Nos. 4 to 6 comprised aqueous dispersions of 45%,52.5% and 57% total solids volume, respectively in a 0.5% carboxymethylhydroxypropylguar solution in water. The total solid volume comprised 3%of the 14-micron micro-particulates of polylactic acid by volume, and97% of macro-particulates of 20/40 Brady sand by volume. The apparentviscosities of Sample Compositions 4 through 6 were measured to be 8.6,17 and 24.4 Pa-second, respectively. The residual stress of SampleCompositions 4 through 6 was measured to be 0, 1.25 and 4 Pa,respectively.

Sample Composition Nos. 7 to 9 comprised aqueous dispersions of 45%,52.5% and 57% total solids volume, respectively in a 0.5% carboxymethylhydroxypropylguar solution in water. The total solid volume comprised 5%of 14-micron micro-particulates of polylactic acid by volume, and 95% ofmacro-particulates of 20/40 Brady sand volume. The apparent viscositiesof Sample Compositions 7 through 9 were measured to be 6.3, 13.8 and14.2 Pa-second, respectively. The residual stress of Sample Compositions7 through 9 was measured to be 0, 1 and 1 Pa, respectively.

The results of this testing are set forth in tabular form below.

TABLE 1 Viscosity of the Dispersion (Pa-second) 45% total 52.5% total57% total solids solids solids volume volume volume Dispersions ofmacro-particulates 13.9 33.8 58.1 of 20/40 Brady sand Dispersionscomprising 97% of 8.6 17.0 24.4 20/40 Brady sand and 3% of 14 micronpolylactic acid micro- particulates Dispersions comprising 95% of 6.313.8 14.2 20/40 Brady sand and 5% of 14 micron polylactic acid micro-particulates

TABLE 2 Residual Stress of the Dispersion (Pa) 45% total 52.5% total 57%total solids solids solids volume volume volume Dispersions ofmacro-particulates 0 9 27 of 20/40 Brady sand Dispersions comprising 97%of 0 1.25 4 20/40 Brady sand and 3% of 14 micron polylactic acid micro-particulates Dispersions comprising 95% of 0 1 1 20/40 Brady sand and 5%of 14 micron polylactic acid micro- particulates

The above example demonstrates, inter alia, that the fluids comprisingmacro-particulates and degradable micro-particulates demonstrateapparent reduction of viscosity and residual stress of the particleladen fluid.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Furthermore, no limitations areintended to the details of construction or design herein shown, otherthan as described in the claims below. It is therefore evident that theparticular illustrative embodiments disclosed above may be altered ormodified and all such variations are considered within the scope andspirit of the present invention. In particular, every range of values(of the form, “from about a to about b,” or, equivalently, “fromapproximately a to b,” or, equivalently, “from approximately a-b”)disclosed herein is to be understood as referring to the power set (theset of all subsets) of the respective range of values, and set forthevery range encompassed within the broader range of values. Also, theterms in the claims have their plain, ordinary meaning unless otherwiseexplicitly and clearly defined by the patentee.

1. A fluid comprising: a liquid component; and a particulatecomposition, the particulate composition comprising macro-particulatesand degradable particulates having a mean particle diameter of at leastabout 20 times smaller than the mean particle diameter of themacro-particulates, wherein the degradable particulates are present inthe particulate composition in an amount sufficient to reduce frictionbetween the macro-particulates.
 2. The fluid of claim 1 wherein theliquid component is selected from the group consisting of a viscosifiedfluid, a foam, an aqueous gel, a viscoelastic surfactant gel, anemulsion; and combinations thereof.
 3. The fluid of claim 1 wherein themacro-particulates are selected from the group consisting of sand,bauxite, a ceramic material, a glass material, a polymer material, athermoplastic fluoropolymer, a nut shell piece, a seed shell piece, acured resinous particulate comprising nut shell pieces, a cured resinousparticulate comprising seed shell pieces, a fruit pit piece, a curedresinous particulate comprising fruit pit pieces, wood, a compositeparticulate, and combinations thereof.
 4. The fluid of claim 1 whereinthe degradable particulates are present in the particulate compositionin an amount in the range of from about 0.25% to about 20% by volume ofthe particulate composition.
 5. The fluid of claim 1 wherein themacro-particulates have a mean particle diameter in the range of fromabout 6 mesh to about 400 mesh.
 6. The fluid of claim 1 wherein thedegradable particulates comprise at least one degradable materialselected from the group consisting of a degradable polymer, a dehydratedcompound, an oil-soluble material, a water-soluble compound, andmixtures thereof.
 7. The fluid of claim 1 wherein the degradableparticulates comprise at least one degradable polymer selected from thegroup consisting of a polysaccharides, a chitin, a chitosan, a protein,an aliphatic polyesters, a poly(lactic acid), a poly(glycolide), apoly(ε-caprolactone), a poly(hydroxy ester ether), apoly(hydroxybutyrate), a poly(anhydride), a polycarbonate, apoly(orthoester), a poly(amino acid), a poly(ethylene oxide), apoly(phosphazene), a poly etherester, a polyester amide, a polyamide,and copolymers and blends thereof.
 8. The fluid of claim 1 wherein thedegradable particulates comprise poly(lactic acid).
 9. The fluid ofclaim 1 wherein the degradable particulate comprises a degradablepolymer and a plasticizer.
 10. The fluid of claim 1 wherein thedegradable particulates comprise at least one oil-soluble materialselected from the group consisting of poly(butadiene), polyisoprene,polyether urethane, polyester urethane, a polyolefin, and copolymers andblends thereof.
 11. The fluid of claim 1 wherein the degradableparticulates comprise at least one water-soluble material selected fromthe group consisting of calcium carbonate, fused magnesium oxide,calcium oxide, and combinations thereof.
 12. The fluid of claim 1wherein the degradable particulates have a mean particle diameter of atleast about 100 times smaller than the mean particle diameter of themacro-particulates.
 13. The fluid of claim 1 wherein the degradableparticulates have a mean particle diameter of at least about 1,000 timessmaller than the mean particle diameter of the macro-particulates. 14.The fluid of claim 1 wherein the degradable particulates have a meanparticle diameter of at least about 3,000 times smaller than the meanparticle diameter of the macro-particulates.
 15. The fluid of claim 1wherein the degradable particulates have a mean particle diameter in therange of from about 10 nanometers to about 30 microns.
 16. The fluid ofclaim 1 wherein the degradable particulates are present in theparticulate composition in an amount in the range of from about 2% toabout 10% by volume of the particulate composition.
 17. The fluid ofclaim 1 wherein the particulate composition is present in the fluid inan amount in the range of from about 50% to about 68% by volume of thefluid.
 18. A particulate composition comprising macro-particulates; anddegradable particulates in an amount sufficient to reduce frictionbetween the macro-particulates, the degradable particulates having amean particle diameter of at least about 20 times smaller than the meanparticle diameter of the macro-particulates.
 19. The particulatecomposition of claim 18 wherein the degradable particulates are presentin the particulate composition in an amount in the range of from about0.25% to about 20% by volume of the particulate composition.
 20. Theparticulate composition of claim 18 wherein the degradable particulateshave a mean particle diameter of at least about 100 times smaller thanthe mean particle diameter of the macro-particulates.
 21. Theparticulate composition of claim 18 wherein the degradable particulateshave a mean particle diameter of at least about 1,000 times smaller thanthe mean particle diameter of the macro-particulates.
 22. Theparticulate composition of claim 18 wherein the degradable particulateshave a mean particle diameter in the range of from about 10 nanometersto about 30 microns.
 23. The particulate composition of claim 18 whereinthe degradable particulates comprise at least one degradable materialselected from the group consisting of a degradable polymer, a dehydratedcompound, an oil-soluble material, a water-soluble compound, andmixtures thereof.
 24. The particulate composition of claim 18 whereinthe degradable particulates comprise poly(lactic acid).